The Ho Chi Minh trail, known within Vietnam as the “Truong Son Strategic Supply Route,” was an elaborate system of mountain and jungle trails linking North Vietnam to its allies in the South Vietnam, Cambodia, and Laos. During the Vietnam War, it served as the primary artery for moving troops, vehicles, and supplies. Comprising more than twelve thousand miles of roads and paths through some of the world’s harshest geography, it was a vital gateway linking a divided nation.
The road network extended from Mu Gia Pass in the north, southward along the heavily forested western slopes of Laos, before entering South Vietnam at the northwestern end of the Plei Trap Valley — the “Valley of Tears” — and points south. It was kept in good condition by 300,000 full-time workers and almost as many part-time farmers, many of whose bodies fill the 72 Vietnamese military cemeteries that testify to the trail’s devastating human toll.
The trail’s history as a line of communication dates back to World War II, when Viet Minh bands trekked the same paths. During the war against the United States, the existing footpaths developed into a highly organized infiltration route for men and supplies. Although the North Vietnamese made limited use of waterways and pipelines, this labyrinth of roads and trails remained throughout the war the heart of their logistic system. As military historian John Prados has pointed out, whereas supplies, ammunition, and weapons could be sent South by boat, “only overland was it possible for men and women to head South and join in combat.”
Despite Hanoi’s attempts to keep the details of its overland infiltration network a secret, by 1960, US knowledge of the route was widespread enough that it became a subject of intelligence predictions. An August 23, 1960 CIA report noted increases in support from the North of the Southern insurgency, citing heightened movement of senior cadres and military supplies such as communications equipment heading south through Laos and Cambodia. Before the year’s end, American military planners were advising the Diem government that it had to gain “firmer control of its frontiers,” to prevent further infiltration by the Viet Cong into South Vietnam.
A September 1966 intelligence study estimated that during the October-November 1965 period, the Ho Chi Minh trail had been disgorging 4500 enemy troops per month and 300 tons of supplies per day. Roadwatch reports and photo reconnaissance verified increased North Vietnamese buildup along the lines of communication from the North into Laos and South Vietnam, revealing new unnumbered roads under construction in the Laotian Panhandle, heading southward.
THE AIR POWER DEBATE
At the earliest stages of major US involvement in Vietnam, military strategists recognized that North Vietnam’s ability to use the Ho Chi Minh Trail to re-supply their forces in the south had to be curtailed. In reviewing their options, their thoughts turned to air power as a means of disrupting the North Vietnamese communications network and forcing Hanoi to enter into serious negotiations for peace with minimal risk to American personnel. Another objective, advocated by officials such as McGeorge Bundy, Johnson’s national security advisor, was to “bolster South Vietnamese morale and reaffirm the credibility of the American commitment to resist revolutionary activity in the Third World.”
Although the aims of the bombing campaign were widely shared, there was much debate over the timing, method, and intensity of the bombing. Robert A. Pape, a military historian who has written extensively on the theory and practice of airpower, identified three competing strategies that were current in 1966: the Civilian strategy, the Air Force strategy, and the Army strategy.
As described by Pape, American proponents of the Civilian strategy believed that North Vietnam could be coerced by gradually increasing threats to its population and economy. This approach called for a limited bombing campaign, characterized by a gradual increase in force, mounting pressure on industry, carefully orchestrated acceleration of tempo, and the promise of inevitable and ultimate destruction.
Key advocates of the strategy-who included Defense Secretary Robert McNamara, Deputy National Security Advisor Walt W. Rostow, and Assistant Secretary of State William Bundy- believed that subjecting the North Vietnamese industrial economy to gradually increasing risk would create a powerful incentive for Hanoi to curtail its support for the insurgency to ensure the survival of its nascent industrial economy. For the civilian leadership, nuclear weapons were only useful to threaten the Vietnamese and their Chinese and Soviet allies, and to hedge against Chinese intervention.
In contrast to the civilian plan, the Air Force strategy was not just to threaten, but to destroy, the North’s industrial base. Proponents such as General Curtis E. Le May, then Air Force Chief of Staff, and his successor General John P. McConnell believed that the destruction of North Vietnam’s industrial war potential would wreak havoc on the country’s political and social fabric. Their goal was to obliterate all industrial and major transportation targets as quickly as possible, to sink the morale of the military and to sow fear among the people. For this strategy, the military wanted relief from politically-imposed “no bombing” zones, not extra firepower to attack such targets derived from nuclear weapons. There was low-level discussion of using nuclear weapons to attack the dykes north of Hanoi in late 1966, but this loose talk never made it into formal evaluation, according to one participant at the time.
The Army strategy focused on undermining Hanoi’s support for the southern insurgency by limiting the flow of men and equipment to the south. Joint Chiefs of Staff Chairman General Earle G. Wheeler, Army Chief of Staff General Harold K. Johnson, and other supporters of the plan wanted to thwart the North Vietnamese ability to succeed on the battlefields of the South by reducing the rate of delivery of support to the Viet Cong below their minimum sustaining level. This counter-insurgency strategy had the most to gain from employing tactical nuclear weapons. In many respects, the JASON study took the Army strategy as its point of reference.
The upshot of the debate was to convince the Johnson administration to initiate a major series of bombing campaigns against North Vietnam known as Rolling Thunder (2 March 1965-31 October 1968). The first phase of the air campaign, carried out in spring-summer 1965, followed the lenient, gradual civilian model and focused on a list of fixed military and transportation targets, one of the most important of which was a 33.3-square mile region known as the Mu Gia pass.
US BOMBING OF THE MU GIA PASS
The Mu Gia pass, a gap in the Truong Son (Annamite) Mountains that formed North Vietnam’s border with Laos, is one of two northern entry points to the Ho Chi Minh trail. To the east, the pass is flanked by a peak of 6,600 feet and on the Laotian side to the west, with a series of mountains in the 4000-4500 foot range. Mu Gia crosses the cordillera at slightly under 1400 feet, making it one of the few passable spots along the rugged Truong Son range. Mu Gia was strategically located some 75 miles as the crow flies from the border of South Vietnam; 80 miles from Tchepone, the site of an airfield with a 4000-foot-by-65-foot runway; 100 miles from the Ban Houei Sane border area, and some 250 miles from vital supply points in the Central Highlands.
Because of its geographic and strategic importance, Mu Gia became a focus of numerous intelligence-gathering missions by “tiger teams” of agents or commandos whose mission it was to penetrate North Vietnam and come up with new data on the trail. By the spring of 1964, the Pentagon was carrying out active target studies, including specific lists of Trail targets and notations of how many sorties would be required to neutralize them. For the Mu Gia pass, the JCS estimated in 1964 that 14 aircraft sorties would be sufficient to neutralize the area. This estimate proved to be highly optimistic.
Navy planes from the USS Coral Sea made the first interdiction strike on the Mu Gia Pass on February 28, 1965. There were 10 Navy A-1H Skyraiders and 14 A-4c Skyhawks, accompanied by two photo planes. The planes dropped bombs that ranged from 500 to 2000 pounds, some set to detonate as long as six days later. The following week, US interdiction targets again included Mu Gia and on March 21, planes from the carrier Hancock struck the Laotian side of the pass. In the summer of 1965, the pass once more appeared on the list of bombing targets. On July 16 and 17, F-105 fighter-bombers dropped 18,000 pounds of munitions on Mu Gia.
Mu Gia and other strategic spots along the Ho Chi Minh trail became a struggle between American attempts to shut down the supply route and Vietnamese ones to keep them going. Defending the route was a core of committed laborers, who protected the trail by making it physically hard to bomb. Over the short term, this meant that the trail was maintained by guerrilla warfare standards, composed of narrow passageways — ranging from a mere six to eight feet wide. Although this limited the transfer of supplies to pack animals and bicycles, it made the area a more difficult target for bombing. Over the long term, Hanoi made preparations for widening parts of the trail to accommodate guns and trucks, which eventually increased the systems supply capacity and allowed the North Vietnamese to respond militarily to US aircraft.
The bombing of Mu Gia continued through the winter, spring, and summer of 1966. According to a May 6, 1966 Time magazine article, during one week-long series of sorties, Guam-based B-52s unloaded 300 tons of high explosives on the pass. The attacks continued through December 1966, maximum-effort strikes using thirty or more huge bombers. It became a very bloody business, and a very considerable number of US aircraft went down along the Trail. According to several POW-MIA sites, between 1965 and 1971, 43 American airmen were shot down over the Mu Gia pass alone.
ROLLING THUNDER AND THE NUCLEAR OPTION
Despite the hundreds of thousands of tons of bombs that were dropped on Mu Gia and other strategic sections of the Ho Chi Minh trail, the Rolling Thunder campaign begun in March 1965 failed in its interdiction objectives for reasons that are still debated by military historians. As early as the summer of 1966, internal review and mounting congressional and public pressure to find coercive leverage over North Vietnam led to a reevaluation of the bombing strategy.
It was against this backdrop of frustration over the inability to interdict the Trail that the possibility of employing nuclear weapons was discussed in Pentagon circles. The JASON study was a response to this loose talk and, although it did not specifically focus on Mu Gia pass, it did analyze interdiction of the Ho Chi Minh trail, including nuclear attacks on bottlenecks such as Mu Gia pass.
The JASONs argued that tactical nuclear weapons (TNW) would be most effective in stopping the enemy from moving “large masses of men in concentrated formations,” against fixed and accurately located targets like bridges, airfields, and missile sites — conditions that were radically different from those that existed along the Ho Chi Minh trail.
Moreover, although they conceded that the use of TNW for interdiction of lines of communication in North Vietnam could be effective under certain circumstances, they determined that it would have required a “huge number of weapons.” Using evidence from a RAND targeting study, which indicated that one TNW equaled on average about 12 non-nuclear attack sorties, they estimated that a completely nuclear Rolling Thunder campaign would have required about 3000 TNW per year. They concluded that such an attack would eventually result in a stalemate, “with the enemy forces retiring into the forests and the US nuclear bombardment running into the law of diminishing returns.”
The JASONs did address the use of TNW to interdict passes in a generic fashion. They stated:
“TNW can be used for interdiction of passes and trails, independently of tree blowdown–Effects of blast, heat, and fire will only be felt by men who happen to be on the trails at the time of the burst; these effects are subject to [certain troop target] limitations. In conclusion, it appears that the interdiction of passes and trails by TNW can be effective only against massive enemy movements on a short time scale, but not against dispersed movements extending over many months or years.”
Balancing the moderate strategic advantages against what they characterized as the “catastrophic” political effects of TNW in Southeast Asia, the authors of the study concluded that the military advantages of unilateral use of nuclear weapons “are not overwhelming enough to ensure termination of the war, and they are therefore heavily outweighed by the disadvantages of eventual bilateral use.”
F. J. Dyson, R. Gomer, S. Weinberg, S.C. Wright, Study S-266: Tactical Nuclear Weapons in Southeast Asia (Institute for Defense Analyses, JASON Division, March 1967).
Mark Clodfelter, The Limits of Air Power: The American Bombing of North Vietnam (New York: The Free Press, 1989).
Robert A. Pape, Bombing to Win: Air Power and Coercion in War (Ithaca: Cornell University Press, 1996).
John Prados, The Blood Road: The Ho Chi Minh Trail and the Vietnam War ((New York: John Wiley and Sons, 1999).
Captain Melvin F. Porter, HQ PACAF Directorate, Tactical Evaluation, CHECO Division Report: Tiger Hound: 6 Sept. 66. Reprinted by Dalley Book Service (Christiansburg, VA), p. 2.
Time, May 6, 1966, p. 16.
USAF AC-119 Gunships: The Ho Chi Minh Trail
John Francis O’Grady, United States Air Force
Scott Winston McIntire, Lieutenant-Colonel, United States Air Force
Photo of the Ho Chi Minh Trail